It is one of the most famous of the five observatories built by Sawai Jai singh in the 18th century. He was progressive and believed in science and technology, and was passionate about astronomy. Situated near the gates of the city palace, Jantar Mantar is the largest stone observatory in the world and has an interesting story behind its construction. Sawai Jai singh sent his emissaries all around the world before the construction began, and they returned with many manuals on astronomy containing technological information. One of these was the copy of La Hire!¦s tables and the king ordered the observatory to be built on these tables. After the construction they realized that was 20 seconds more accurate than the table!